Invariability in position of the Otx2 posterior expression boundary. Double detection of otx2 and hoxb1b transcripts in wild-type embryos at 60% (A), 80% (B) and bud (C) stages. hoxb1b anterior limit defines the r3/r4 boundary. The gap between the two expression domains remains constant, arguing against an anterior shift in otx2 expression during late gastrulation. (D-I) Rostral expansion of cerebellum in OtH embryos. Lateral (D-G) or dorsal (H,I) views of cerebellar areas from wild-type (D,F,H) and OtxH (E,G,I) embryos, showing expansion of pax6 (D,E) and reelin (F,G) expression in granule cells, and zebrin (H,I) in Purkinje cells in OtxH embryos. (J-O) Rescue of granular cells in OtxH embryos lacking Fgf signal. (J-K) Lateral views, anterior towards the left, of 12-somite stage brains showing fgf3 expression, which is never detectable in the isthmus of fgf8–/– mutant embryos (arrows indicate the presumptive isthmic area). (L-O) Lateral views of wild-type (L), OtxH (M), wild-type treated with SU5402 (N) and OtxH treated with SU5402 (O) whole-mount embryos, showing atoh1a expression. Granule cell precursors in the upper rhombic lip in wild type (arrow on dorsal view in inset L) are lost after inhibition of Fgf signal (arrow on dorsal view in inset N). The residual expression in lateral and lower rhombic lip is not giving rise to granule precursors. The upper rhombic lip population increases in OtxH (arrow on dorsal view in inset M), and is kept in OtxH+SU5402 (arrow on dorsal view in inset O).
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